Floating roof for liquid storage apparatus



J. H. WIGGINS 2,287,213

FLOATING ROOF FOR LIQUID STORAGE APPARATUS June 23, 1942.

Filed May 10, 1939 INVENTOR; JOHN H. WIGGINS M ATTORNEY means.

Fatenied June 23, I 1942 were noa'rmo noon Eon neon) s'romcn mana'ros John Wiggins, Chicago, Ill.

Application May 10,1939, Serial No. 272,748

1 claim. 101.220-26) This invention relates to floating tank roofs of the kind that are used with storage tanks of relatively great diameter, and which consist of a metal deck combined with a metal pontoon or equivalent auxiliary buoyant means that imparts additional buoyancy to the deck.

that when the roof is floating on the liquid in the tank, the deck plates will be in tension, and sloping upwardly from near the periphery towards the center of the roof, thereby causing an eccentric load imposed on one sideof the roof to be transmitted directly across to the other side One object of my present invention is to provide a floating roof'for large size storage for example, a tank having a. diameter in excess of 100 feet, that is cheaper to build and which contains considerable less metal and is lighter in weight than metal floating tank roofs of conventional design.

Another object is to provide a large size floating roof of the pontoon type, whose deck and auxiliary buoyant means are combined in a novel manner that insures eccentric loads being carried effectively from one side of the roof to the other, notwithstanding the fact that the roof is not equipped with trusses or with a trussing Another object is to provide a floating metal roof which is of such construction or design that it is incapable of collecting and holding a large load of rainwater, and whose top area is made up of self-draining surfaces of a .sufliciently sharp, pitch or slope to prevent-puddles of water from standing on'the top side of the roof and injuring the paint used to protect the roof plates against corrosion, either when the roof is floating on the liquid in the tank, or when the tank is empty,

and the roof is supported by the bottom of the tank.

And still another object is to provide a floating tank roof, which, in addition to having the 'desirable features or characteristics above stated, is of such construction or design that it is not necessary to equip it with adjustable legs or sup-.

porting devices for sustaining the weight of the roof when the tank is empty, and for holding the roof spaced far enough above the bottom of the tank to permit workmen to enter the tank and remove sediment that has collected on' the bottom of the tank. I,

To this end I have devised the floating tank roof herein shown and described, which roof comprises the following three main elements,'

5 ploying the pontoons for this I am able to. omit the adjustable supporting legs -with which floating roofsof conventional design height or depth, and the deck portion is combined with or attached to said pontoons in such a way,

of the roof, through the deck plates which constitute the sole connection between the two pontoons. By constructing the roof in this manner I overcome the necessity of equipping the roof with a truss or trussing means to transmit eccentric loads from one side of the roof to-the other, and hence, I reduce the cost of the roof,

' I reduce the amount of metal in the roof, and I rapidly carry oil water that falls'on the roof,

either when the roof is floatingon the liquid, or when the roof is supported-by the bottom of the tank. By designing or constructing the roof so. that it is incapable of collecting and-holding an excessive or emergency load of rainwater, I overcome the necessity of building the roof strong enough to take care of an emergency rain load, and thus, I eilect an additional saving, both in the cost and in the weight of the roof. Preferably, the pontoons are arranged on the underside of the roof, and the center pontoon is made considerably deeper or higher than the peripheral pontoon, thereby causing the deck portion to slope downwardly and outwardly, .at a fairly sharp pitch or angle, from the central portion of the roof to a valley located adjacent the periphery of the roof, and provided with drains of such number, capacity and rate of discharge as disposal of even a heavy cloudtank, and thus provides a space on the underside, of the deck for workmen engaged in removing the tank. vBy emsediment from the bottom of additional purpose,

are usually equipped, and I accordingly effect still another saving in the cost and weight of the roof. v

Figure 1 of the drawing is a vertical transverse sectional view of a liquid storage apparatus equipped with a floating roof embodying mwpresent invention, showing the roof floating upon the liquid confined in the container of the apparatus.

I of liquid at conflned in the tank or container B.

As previously stated, the primary purpose of my invention is to provide a highly practicable metal floating root for large size storage tanks, and accordinsly, the container B may be considered as a conventional oil storage tank having a diameter 01' 100 feet or more. In the preferred form of my invention herein illustrated the root is of the pontoon type, and is provided with pontoons, or an equivalent buoyant means, and combined with the deck portion that, irrespective or any load that may be imposed upon the root (a load or rainwater or snow), the deck A will maintain its approximately original shape or form, and any eccentric load imposed on one side 01 the roof will be carried to the other side or the root through the deck plates. In the particular form or my invention herein illustrated, the root is equipped with a center pontoon C, and a peripheral pontoon D, separated from each other by an annularspace, the center pontoon being 01 stifl construction and of greater height or depth than the peripheral pontoon D, so as to insure that'the deck of the root will maintain a substantially dome torm;-- in other words, will remain in a position with the central portion of the deck disposed in a higher horizontal plane than the peripheral portion or the deck. In the root herein illustrated the pontoons C and D arearranged on the underside or the deck, and the deck portion A is so constructed that the root comprises an inclined portion I at the peripheral edge oi the roof that slopes oppositely to a downwardly and outwardly inclined portion 2 that .constitutes themajor area oi the top side of the roof, said inclined portion l sloping downwardly and inwardly and then merging into the downwardly and outwardly inclined portion 2, thus forming in effect a valley near theouter edge of I the roof that is provided with numerous drains E of any herein illustrated being of the inverted syphon type, commonly used on Wiggins floating roofs. when the-tank contains suflieient liquid to float the roof, most oi! the deck portion A reries the load to the opposite side of the annular pontoon through the deck plates. From the foregoing it will be understood that in my improved roof, the annular space between the two pontoons is bridged by a plate-like deck portion A, of single thickness, that is always in tension, and which constitutes the sole connecting means between the peripheral pontoon D and the center pontoon C, which exerts a constant upward pressure on the deck portion A and holds it in a downwardly and outwardly sloped position.

so constructed suitable type or kind, the drains E By varying theheight or the center pontoon, and hence, the pitch of the deck, any desired proportion of the deck and itsload may be carried by the center pontoon, thus giving accurate control of the compression set up in the annular pontoon D by the weight of the deck, and any superimposed loads which are carried bythe annular pontoon. In other words, the radius of the point of contraflexure of the deck may be controlled by the height of the center pontoon. The drains E, are of course, preferably placed at the lowest point of the deck under normal conditions, and while I prefer to construct the deck so that it is provided at its extreme outer edge with a downwardly and inwardly inclined portion,

1, as previously described, this particular shape or form of the deck is not essential.

When the tank B is empty, or substantially so, the floating roof above described is supported by the bottom of the tank, usually by supports 3 on the tank bottom, that hold the pontoons plurality of vertically-disposed, open-ended, tubular members 4, that project upwardly through the center pontoon C, so that steam supply hoses 5 may be attached to same to discharge steam into the tank. Normally, the upper ends of the tubular members 4 are closed by removablecaps 6, as shown in Figure 1. Owing to'the fact that.

the pontoons C and D are of considerable height or depth, the space, on the underside of the deck 0, when the roof is supported by the bottom of th tank, is high enough to permit workmen to enter said space to remove sediment 'or foreign matter that collects on the bottom of the tank.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

A floating tank roof of relatively great diameter, composed of a deck portion of a single thickness, made up of metal plates joined togethcr, a stiff annular pontoon at the periphery ,of the rooi attached adjacent its upper end to a said deck portion, a relatively large diameter mains in a plane considerably higher than the peripheral portion or the roof, due to the greater height or depth of the center pontoon than the peripheral pontoon, and due to the upward pressure eierted on the under side or the deck portion A by the gases confined in the relatively deep space above the-surface or the liquid in proximity to the center pontoon C. Under uniform top loading (such as snow) the annular pontoon D sinks as much or niore than the stifl center pontoon 0, thus maintaining the downward and outward slope o! the deck A for drainage. Under a load concentrated at the periphery oi the roof (such as a snow driit) the annular pontoon D sinks much lower than the center pontoon, which throws the deck plates into tension, dips the center pontoon, which tightens the portion.

pontoon of still construction arranged at the center of the roof and attached adjacent its -upper end to said deck portion, saidpontoons being separated from each other by'an annular space that is bridgedby the deck portion and the center pontoon being considerably deeper than the annular pontoon and having its top disposed in a considerably higher horizontal plane than the top or the annular pontoon, said deck portion and pontoons being connected together and disposed in such relative relationship that when the root is floating on the liquid in the tank said deck portion will always be in tensionand will cause eccentric loads to be carried fromone side of the roof to the other through the plates of said deck John H. WIGGINS. 

